Theoretical study of the structure and stability of oxovanadate complexes with MO₄ ⁿ⁻ tetraoxo anions in the inner and outer spheres of the V₂₀O₅₀ cluster

Abstract

The energies and structural and spectroscopic characteristics of endohedral and exohedral isomers of oxovanadate complexes with MO₄ ⁿ⁻ tetraoxo anions located in the inner and outer spheres of the V₂₀O₅₀ cluster have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, among the endohedral MO₄@V₂₀O₅₀ ⁿ⁻ clusters with strong multiply charged anions (VO₄ ³⁻, CrO₄ ²⁻, PO₄ ³⁻, SO₄ ²⁻, BO₄ ⁵⁻, etc.), the isomer in which a distorted “guest” tetrahedron MO₄ is displaced from the cluster center and bonded to the V20O50 cage through two internal oxygen bridges M−O*−V is the most favorable one. Among the exohedral analogues MO4 · V₂₀O₅₀ ⁿ⁻, the most favorable isomer contains the guest in the capping position bonded to the cage from the outside through three external M−O−V bridges. The latter isomer is more favorable than the former; however, the “exo–endo” transition between them for the clusters with multiply charged anions is accompanied by small changes in energy of ∼2−10 kcal/mol. Singly charged perchlorate and perbromate anions ClO₄ ^- and BrO₄ ⁻ in the inner sphere of V₂₀O₅₀ are unstable: during optimization, they are “reduced” with decomposition into atoms and concurrent “inner-sphere oxidation” of V₂₀O₅₀ to V₂₀O₅₄ with four peroxide cage bridges V−O−O−V. Charge transfer and specific features of the host–guest interaction in oxovanadate complexes and trends in the properties of endo- and exohedral isomers as a function of the charge and bond character of guest anions are discussed.